The present invention relates to heat exchangers, and more particularly, to a fin-and-tube type heat exchanger formed of aluminum suitable for use as an evaporator of an air cooling system for automotive vehicles having a joint construction that can be advantageously provided by brazing.
Referring to FIG. 1, a plurality of fins 3 are arranged in superposed relation between upper and lower end plates 1 and 2 in such a manner that the spacing between the fins 3 is kept constant by a plurality of cylindrical flanges 4 provided to each of the fins 3. U-bend tubes 5 extend from the lower end plate 2 through openings formed therein with the same pitch diameter as openings formed in the fins 3 and penetrate the upper end plate 1 through openings similar to those formed in the lower end plate 2, to project upwardly from the upper end plate 1. Each of the U-bend tubes 5 projecting upwardly from the upper end plate 1 has a U-bend tube 6 of smaller length than the U-bend tube 5 joined thereto by brazing, so that the adjacent U-bend tubes 5 are connected together to provide a serpentine passageway for a refrigerant to flow therethrough.
In joining the U-bend tube 6 to the U-bend tube 5, it has been the usual practice to carry out the operation in a manually operated torch brazing process or a furnace brazing process and FIG. 3 shows the shape of a brazed joint produced generally in the art. As shown, an assembly of the U-bend tubes inserted in the openings in the fins 3 is supported on a support 7 which has a bottom of the U-shape of the tube 5 resting thereon, and a rod 8 having a ball is inserted in the tube from its upper end to be force fitted therein, to thereby expand the tube 5 and secure the tube 5 to the upper and lower end plates 1 and 2 in a single operation. At this time, when the ball has reached the lower end of the tube at the lower end plate 2 and tube expansion has made a substantial progress, a tube end flaring punch 9 is inserted in the tube 5, to form a flare 10 at the end. However, the flare 10 is merely formed on the upper end plate 1 and has a shape and configuration which makes it difficult to obtain dimensional accuracy. FIG. 4 shows a tube 6 joined by brazing to the tube 5 formed with a flare of low dimensional accuracy.